C++ 错误 具有类型“const sort”的表达式会丢失一些 const-volatile 限定符以调用“bool sort::operator ()(int,int)” 如下：环境 vs2019 内容：set内置函数排序

C++ 错误 具有类型“const sort”的表达式会丢失一些 const-volatile 限定符以调用“bool sort::operator ()(int,int)”  如下：

环境 vs2019

内容：set内置函数排序

 1 #include <iostream>
 2 #include<set>
 3 #include<string>
 4
 5 using namespace std;
 6
 7
 8 class sort
 9 {
10 public:
11     bool operator()(int v1, int v2)
12     {
13         return v1 > v2;
14     }
15 };
16
17
18 void test01()
19 {
20     set<int>s1;
21     s1.insert(30);
22     s1.insert(10);
23     s1.insert(50);
24     s1.insert(20);
25     s1.insert(40);
26
27     for (set<int>::iterator it = s1.begin(); it != s1.end(); it++)
28     {
29         cout << *it << " ";
30     }
31     cout << endl;
32
33     set<int, sort>s2;
34     s2.insert(30);
35     s2.insert(10);
36     s2.insert(50);
37     s2.insert(20);
38     s2.insert(40);
39
40     for (set<int, sort>::iterator it = s2.begin(); it != s2.end(); it++)
41     {
42         cout << *it << " ";
43     }
44     cout << endl;
45
46
47 }
48 int main()
49 {
50
51     test01();
52
53     system("pause");
54     return 0;
55 }

//改正   在仿函数中加入const

#include <iostream>
#include<set>
#include<string>

using namespace std;

class sort
{
public:
    bool operator()(int v1, int v2) const
    {
        return v1 > v2;
    }
};

void test01()
{
    set<int>s1;
    s1.insert(30);
    s1.insert(10);
    s1.insert(50);
    s1.insert(20);
    s1.insert(40);

    for (set<int>::iterator it = s1.begin(); it != s1.end(); it++)
    {
        cout << *it << " ";
    }
    cout << endl;

    set<int, sort>s2;
    s2.insert(30);
    s2.insert(10);
    s2.insert(50);
    s2.insert(20);
    s2.insert(40);

    for (set<int, sort>::iterator it = s2.begin(); it != s2.end(); it++)
    {
        cout << *it << " ";
    }
    cout << endl;

}
int main()
{

    test01();

    system("pause");
    return 0;
}